1. Field of the Invention
The present invention relates to a method of feedback-controlling the idling speed of an internal combustion engine and, more particularly, to an idling speed feedback control method wherein the magnitude of the electrical load on the engine, when electrical load equipment or devices are in an operative state is accurately detected, and supplementary air is applied in accordance with the magnitude of electrical load, to thereby eliminate any speed control delay.
2. Description of the Prior Art
An idling speed feedback control method is known in which a target idling speed is set in accordance with the load conditions of an engine, and the difference between the target idling speed and the actual engine speed is detected. The engine is then supplied with an amount of auxiliary air which corresponds to the magnitude of the detected difference so that the difference becomes zero, thereby controlling the engine speed so that it is maintained at the target idling speed, e.g., Japanese Patent Laid-Open No. 98,628/80.
In the above-described method, if an electrical load device, such as a headlight or an electrically-operated radiator cooling fan motor, is actuated during idling speed feedback control (referred to as "feedback mode control", hereinafter), an alternating current (AC) generator which supplies electric power to the actuated electrical load is actuated. As a result, the operation of the AC generator increases the engine load, resulting in a lowering of the engine speed. The lowered engine speed is shortly returned to the target idling speed by virtue of the feedback mode control. However, when a large electrical load is applied to the engine, the engine may be stalled, or it may become impossible to smoothly engage the clutch when the vehicle is started simultaneously with increasing of the electrical load.
In view of the above, an engine speed control method has been proposed by the applicant of the present invention in Japanese Application Laid-Open No. 197,449/83, in which the ON-OFF state of each of a plurality of electrical load devices is detected, and at the same time, as the ON state of each electrical load device is detected, the valve-opening duration of a control valve which controls the auxiliary air amount is increased by a predetermined period of time in accordance with the magnitude of the electrical load, whereby the delay in the auxiliary air amount control is minimized, thereby improving driveability.
Presently, however, internal combustion engines are equipped with a great variety of equipment which are electrical loads in order to improve the operation performance of the engines and further to ensure safe traveling of vehicles equipped with such engines. For this reason, it is necessary to provide a number of sensors and input ports corresponding to the number of the electrical load devices in order to detect the ON-OFF state of each of the electrical load devices. Further, it is necessary to store a predetermined valve-opening duration for the auxiliary air control valve associated with each electrical load device. In consequence, there is a need for a more complicated control program, which results in an increase in the memory capacity of the controller. As a result, the cost of the controller is significantly increased. In order to avoid these disadvantages, a method may be adopted in which, only some of the electrical equipment, for example, some of the which apply a heavy load to the engine are monitored for the purpose of control, and the electrical load correction of the auxiliary air amount is effected only when one of the monitored electrical devices is turned ON or OFF. In this method, however, when one or a plurality of the electrical load devices which are not monitored are turned ON or OFF simultaneously with a monitored electrical load device, because of the feedback mode control delay, the engine speed is temporarily lowered or raised, which makes it difficult to maintain the engine speed at or in the vicinity of the target idling speed.